The attackers who crippled Ukrainian power operators in December probably committed attacks shortly before against a mining company and a railway operator, Trend Micro said Thursday.

The security company said its latest technical research shows that the same malware -- dubbed BlackEnergy and KillDisk -- were probably used in the earlier actions. It didn't name the targets of those attacks, which took place in November and December.

"There is remarkable overlap between the malware used, infrastructure, naming conventions, and to some degree, the timing of use for this malware," wrote Kyle Wilhoit, a senior threat researcher.

The cyberattacks against the two utilities, Prykarpattyaoblenergo and Kyivoblenergo, have caused widespread concern in the security community, which has warned that attacks against industrial control systems could cause great damage.

Kyivoblenergo said 80,000 customers lost power for six hours after 30 substations went offline. Service was restored after operators took manual control and closed circuit breakers.

The malware used in the attacks, known as Black Energy, has been linked by the security firm iSight Partners to a group nicknamed the Sandworm Team, which is suspected to be from Russia. Relations between Ukraine and Russia have been tense since Russia annexed Crimea in 2014.

BlackEnergy probably infected the large mining company, according to Wilhoit. The malware in the earlier attack communicated with the same command-and-control servers as the tools that infected the two utilities, he wrote.

The mining company also was infected with several versions of KillDisk, which is designed to make a computer unusable by overwriting the Master Boot Record (MBR), the first sector of a PC’s hard drive. KillDisk also overwrites files with junk data.

"While none of the exact samples in the prior utility attacks appear to have been used against the mining organization, the specific samples witnessed perform the same exact functionality as those witnessed at the Ukrainian power utilities, with very little difference," Wilhoit wrote.

There also are indications that KillDisk affected the railway operator. Trend Micro believes that BlackEnergy was probably on the railroad's systems, too.

"The infections in the mining and train companies may have just been preliminary infections where the attackers are just attempting to test the code base," Wilhoit wrote.